The present invention is directed to the use of selected modified starches, prepared by cooking at high temperature and pressure, as natural adhesives in the manufacture of cigarettes.
Cigarettes are generally comprised of a cigarette rod and most often a filter or plug. The cigarette rod consists of a stream of tobacco wrapped in a paper tube, the paper tube being glued along one longitudinal edge with a suitable adhesive (side seam or lap seal). The filter or filter plug generally consists of a crimped textile tow of cellulose acetate fibers treated with a plasticizer and wrapped into a cylindrical form with paper. The center of the paper is attached to the fibers using an adhesive (centerline adhesive) and the paper is then wrapped around the plug rod, overlapping and attaching itself with an adhesive (overlap adhesive) to form the cylindrical filter plug. The filter or plug is then attached to the cigarette rod by wrapping another paper (tipping paper) which contains an adhesive (tipping adhesive) around the plug and overlapping it with an aligned rod.
Most cigarette manufacturing processes involve high speed operations (2000-12000 cigarettes per minute) where the adhesive is typically applied by nozzle (side seaming, center-line and overlap), paste wheel (side seaming) and by rollers (filter tipping). Adhesives used in these operations are generally synthetic emulsions but because of increasing interest and tobacco regulation requirements in different countries, natural type adhesives are being sought to replace the synthetics.
Starch has long been used as an adhesive material in various applications such as case and carton sealing, laminating, tube winding, papermaking, etc., as described in Starch: Chemistry and Technology, second edition by R. Whistler, J. Bemiller and E. Paschall, 1984, pp. 593-610. Dextrins and thin-boiling starches are disclosed as useful as side seam adhesives but generally at lower solids than being required at current high speed manufacturing operations.
The cooking of starch at high temperature and pressure in continuous operations is well known as disclosed in Whistler noted above. One such method disclosed in Japanese Patent No. 57-11579, published Mar. 5, 1982, involves continuous adhesive manufacturing of natural or synthetic adhesive materials using high pressure heating and forced stirring.
Despite continued developments and improvements for adhesive properties and technological advances in the manufacturing techniques for producing adhesives, there still is the need for a natural adhesive material which will satisfy the requirements of current cigarette production. This has not been easy to accomplish particularly because of the demanding high speed operation and the required properties that adhesive materials used in these operations must possess including flow or fluidity, drying speed, cohesiveness, bonding strength, viscosity stability, machinability and other rheological characteristics.